CRT (cathode ray tube) display devices are generally characterized by a non-linear relationship between the applied input voltage and the output luminance (light intensity) for any given pixel. This relationship can be approximated by the exponential function, luminance=(voltage) (gamma), where voltage is normalized to one. The relationship is non-linear for many display devices, because gamma is generally not equal to one. As a result, the amount of light emitted from a phosphor on the screen tends to be less than what it should be, given the applied voltage. Hence, an image showing a gradual transition from black to white (a "linear ramp") will generally appear very dark. This effect is well understood. In fact, video cameras are generally designed to output a signal that is "gamma corrected", so that a linear ramp will be displayed as a linear ramp.
For many applications involving image processing, however, the accurate display of images is essential. Accordingly, gamma determination and correction becomes crucial for such applications. Some image processing software applications allow a computer user to enter the gamma of the monitor, so that images can be gamma corrected before display. However, the user must first know the value of the gamma. Graphics arts professionals often use physical instruments to measure the gamma and other monitor characteristics. However, the typical user does not have access to such equipment. Other programs allow a user to adjust the gamma, but the user must still determine the overall gamma correction himself, taking into account any gamma correction that may already be included in the images to be displayed. In addition, such programs often do not allow gamma correction to be performed with high accuracy. What is needed, therefore, is an easy, accurate way for an ordinary user to determine the gamma of a display device without the use of a separate physical measuring device.